Method of making ceramic cylinders



L z l I I W. A. DANIEL METHOD OF MAKING CERAMIC CYLINDERS Filed April15, 1957 L HHHHH. w \%av Llllllllllllllllll llllll R E m M ML V4 0 m W n1 A A d W Y A B f a 2,914,834 r F MAKINGCERAMIC CYLINDERS William A'.Daniel, Van Nuys, Califi, assignor to Bendix 1 Aviation Corporation,North Hollywood, Calif., a corwporation of Delaware Application April15,1957, Serial No. 652,893

' Claims. c1. 25-151 This 'invention relates to the manufacture oftubular ceramic objectsandhas particular application to thinwalledhollow "cylinders of-ceramic material that shrink appreciablyduringfiring;

.A' general object of the; invention is to reduce distortion of tubularceramic object's during firing. 1

It is well known that many ceramic materials become quite soft du ringfiring and distort in response to relatively slight fofce's. T oredu'cethe distorting force of gravity on hollow cylinders, they are fired invertical position while resting on a flat surface. However, if thecylinder shrinks, inward movement of the base is resisted by frictionibetween it and the supporting surface so that the lower endisj oftenbelled or oval, and a substantial portion must be cut off and discarded.This belling has been reduced by supporting the cylinder upon ashrinkage ring of the same ceramic and of substantial radial thicknessduring firing, but shrinkage rings are expensive and are not alwayssuccessful.

In accordance with the present invention, an end wall of the sameceramic material is formed on the base end of the cylinder. This endwall tends to shrink during firing at the same rate as the cylinder, andhas sufficient strength, by virtue of its large radial dimensions, toovervcome the frictional resistance of the supporting surface.

This substantially eliminates any distortion of the cylinder from a truecylindrical shape during firing, after which the lower end is cut offclose to the end wall.

. tion is a method of forming a suitable end wall on a centrifugallycast cylinder.

Other objects and features of the invention will be apparent from thefollowing detailed description taken in connection with the drawing, inwhich:

Fig. l is a longitudinal sectional view illustrating the centrifugalslip-casting of a hollow ceramic cylinder.

Fig. 2 is a schematic diagram showing a mold containing a centrifugallycast cylinder positioned on a porous slab, ready for the casting of anend wall thereon.

Fig. 3 is a diagram like Fig. 2, with the end wall poured.

Fig. 4 is a schematic diagram showing a cylinder with an end wallpositioned in a mufiie for firing.

Fig. 5 shows a finished cylinder with the end wall removed.

Fig. 1 shows a portion of a centrifugal casting machine that may be usedto produce open-ended, hollow ceramic cylinders. It comprises a porouscylindrical mold 10, which may be of plaster of Paris, and is supportedbetween two end walls 11 and 12.. The end walls have annular grooves 11aand 12a, respectively, for receiving the ends of the mold 10. Gaskets11b and 12b may be positioned in the annular grooves 11a and 12a,respectively, to effect a fluid seal. The end walls 11 and 12 aresupported on an arbor 13 having nuts 14 and 15 bearing against the outersurfaces of the end walls 11 and 2,914,834 Patented Dec. 1, 1959 2 12,respectively, for securing them tightly against cylindrical mold 10. Thearbor 13 has a central passage 13a extending from the end wall 11 pastthe end wall 12, and has radially extending slots 13b extendingtherefrom; between the end walls 11 and 12 for the discharge ofslipvinto the mold. Slip is supplied to the passage 13a through a hollowbushing 18 encircling the shaft beyond the mold end wall 12 andcommunicating with the passage 1341 through radial holes 130 therein.The bushing 18 remains stationary while the arbor 13 rotates, and issealed with respect to the arbor by washers 17 of resilient ma; terialwhich are compressed between the opposite ends of the bushing 18 and apair of ball thrust bearings, 16, 16. i In operation, the bushing 18 isconnected to a source of slip through a suitable line connected to anipple 18a on the bushing 18, and, While the arbor 13 is rotated by anysuitable mechanism, a desired quantity of slip is forced through thenipple 18a, the hollow bushing 18, the passage 13a in the arbor, and outthrough the slots 13b into the rotating mold. The slip is quicklyforced.

by the centrifugal force into a layer 20 which is hereinafter referredtoas the casting or the cylindrical casting. The spinning of the mold iscontinued until the casting 20 has been sulficiently driedby transfer ofwater from the slip] into the porous mold 10 to. make the castingself-support the casting 20 adhering thereto is removed from the casting apparatus and is set in verticalposition on a porous slab, ofmaterial such as plaster of Paris, as indicated at 21 in Fig. 2.

It will be observed that by virtue of the annular grooves 11a and 12a inthe mold end walls 11 and 12 of Fig. l,

the cylindrical mold 10 extends beyond the end of the casting 20.

An end wall 22 is then formed on the lower end of the casting 20, whilethe latter is in semi-wet condition, by pouring a quantity of slip intothe cylinder while positioned as shown in Fig. 2. The slip flattens outby its own weight, as shown in Fig. 3, and dries by absorption ofmoisture therefrom intothe porous slab 21 to form an end wall 22. Theassembly of the casting 20 and the end wall casting 22 is permitted todry in the cylindrical mold 10 and on the porous slab 21 until theydetach themof the casting 20 and the end Wall 22 may be then lifted offthe slab 21.

The assembly of the casting 20 and 22, after further drying ifnecessary, is then placed, as shown in Fig. 4, on a refractory slab 25which is covered with a layer of leveled refractory sand 26. The castingis enclosed with a refractory tube or muffle 27 and a top plate 28 ofrefractory material. The entire assembly is then placed in a suitablekiln and fired.

As previously indicated, some ceramic materials become quite soft duringthe firing operation, and also contract substantially. This contractionnormally results in uniform radial contraction of the casting 20,provided such contraction is not impeded by any resistant forces. When acasting 20 without an end wall 22 is supported directly on a refractoryslab, the radial contraction at the lower end of the casting isrestrained, and belling or distortion from true concentric shape oftenresults. However, the end wall casting 22 prevents such distortion,because it has sufficient body to overcome its frictional resistance tomovement along the refractory slab 25, and carries the lower end of thecasting 20 with it.

It is important that the end wall 22 extends below the end of thecasting 20, and not merely be joined to the inner surface of the casting20, because the bond between the base 22 and the casting 20 may then bethev lower end of the cylinder 20, it has no tendencyto pull.

radially inwardly away from the cylinder 20 during the firing operation.

1 After the firing has been completed and the assembly has cooled, theend wall 22 and a small portion of the casting 20 may be sawed off, asshown in Fig. 5, to leave the desired open-ended cylindrical ceramicshape. The small portion of the casting 20 that is removed with the endwall 22 is negligible compared with the portion that must often bediscarded when the cylinders 20 are fired without the end wall 22 toreduce belling and other distortion.

Although for the purpose of explaining the invention a particularembodiment thereof has been shown and described, obvious modificationswill occur to a person skilled in the art, and I do not desire to belimited to the exact details shown and described.

I claim:

1. The method of reducing distortion in a hollow ceramic cylinder duringfiring thereof comprising: forming at one end of the cylinder while itis in semi-wet condition a ceramic end wall extending across the end andinbonding contact with the end surface of the cylinder; drying theassembly of cylinder and end wall; firing said assembly with said endwall resting on a horizontal supporting surface and the cylindersupported in vertical position entirely on said end wall; and removingsaid end wall.

2. The method of claim 1 in which said end wall is formed on the end ofthe cylinder by pour casting.

3. The method of claim 1 in which said end wall extends into saidcylinder in contact with a zone of the inner surface thereof nextadjacent the end thereof.

4. The method of producing a hollow ceramic cylinder comprising:centrifugal slip-casting a ceramic cylinder in a hollow absorbentcylindrical mold having a removable end closure ext'endinginto the moldwhereby one end of the cylinder is-spaced from the adjacent end of themold; removing said end closure;'supporting said mold with the cylindertherein in vertical position on a flat absorbent surface with saidadjacent end'of the mold resting on said surface; casting a-ceramic endwall on said cylinder by pouring slip-into. said. cylinder to a depthsuflicient to fill said mold at least to said one end of said cylinder;drying the assembly of cylinder and end wall; firing said assembly withsaid end wall resting on a horizontal supporting surface and thecylinder supported in vertical position entirely on said end wall; andremoving said end wall. I

5. The method of claim 4 in which said slip is poured to a level abovesaid one end of said cylinder, whereby the end wall joins thecylinderboth over the surface of said one end and over a zone of theinner surface adjacent said end.

References Cited in the file of this patent UNITED STATES PATENTS1,612,916 Gorton Jan. 4, 1927 1,786,385 Andrews Dec. 23, 1930 1,920,589Payne Aug. 1, 1933 2,173,107 Gould Sept. 19, 1939

